In recent years, a semiconductor memory utilizing a resistance variable element as a memory element, such as a PRAM (phase-change random access memory) or an MRAM (magnetic random access memory), has been attracting attention and being developed. The MRAM is a device which performs a memory operation by storing “1” or “0” information in a memory cell by using a magnetoresistive effect, and has features of nonvolatility, high-speed operation, high integration and high reliability.
One of magnetoresistive effect elements is a magnetic tunnel junction (MTJ) element including a three-layer multilayer structure of a storage layer having a variable magnetization direction, an insulation film as a tunnel barrier, and a reference layer which maintains a predetermined magnetization direction.
The resistance of the MTJ element varies depending on the magnetization directions of the storage layer and the reference layer, it takes a minimum value when the magnetization directions are parallel, and takes a maximum value when the magnetization directions are antiparallel, and information is stored by associating the parallel state and antiparallel state with binary information “0” and binary information “1”, respectively.
Writing of information into the MTJ element involves a magnetic-field write scheme in which only the magnetization direction in the storage layer is reversed by a current magnetic field that is generated when a current flowing is flowed through a write line, and a write (spin injection write) scheme using spin angular momentum movement in which the magnetization direction in the storage layer is reversed by passing a spin polarization current through the MTJ element itself.
In the former scheme, when the element size is reduced, the coercivity of a magnetic body constituting the storage layer increases and the write current tends to increase, and thus it is difficult to achieve both the miniaturization and low electric current.
On the other hand, in the latter scheme (spin injection write scheme), spin polarized electron to be injected into the MTJ element decreases with the decrease of the volume of the magnetic layer constituting the storage layer, so that it is expected that both the miniaturization and low electric current may be easily achieved.